Field of the Invention
The present invention relates to a polymerization apparatus for polymerizing a monomer having an ethylenically unsaturated double bond that carries out the polymerization while the reaction mixture is circulated through a heat exchanger that is arranged separately from the polymerization vessel.
Description of the Prior Art
Polymerization of a monomer having an ethylenically unsaturated double bond is carried out in such a manner that a polymerization medium, such as water, a dispersant, a polymerization initiator, the monomer having an ethylenically unsaturated double bond, and, if required, other various additives are charged into a polymerization vessel equipped with a jacket and a reflux condenser, then the inside temperature of the polymerization vessel is elevated, and the polymerization reaction is carried out while the temperature is kept at a constant temperature. To keep the inside of the polymerization vessel at a constant temperature during that polymerization reaction, since it is required to remove the heat of the polymerization reaction, cooling water is circulated through the jacket and the reflux condenser.
In recent years, in order to improve productivity, it is carried out (1) to make a polymerization vessel large and (2) to shorten the polymerization time per batch. However, as the polymerization vessel is made large, the rate of the heat transfer area to the reaction mixture per unit volume is decreased, and therefore the above-mentioned conventional method of removing the heat of polymerization reaction is insufficient in heat removing capacity. Further, if the polymerization time per batch is shortened, the exotherm rate of the polymerization reaction per unit time increases, and therefore the heat removing capacity becomes further insufficient.
To overcome this disadvantage, several methods are suggested and, among them, an effective method includes a method wherein a reaction mixture is circulated through a heat exchanger arranged outside a polymerization vessel (see Japanese Pre-examination Patent Publication (kokai) Nos. 24991/1979, 47410/1981, and 32606/1983 and Japanese Patent Publication (kokoku) No. 11642/1989). This method is quite effective in that the rate of the heat transfer area to the reaction mixture per unit volume can be made large.
However, this method has a problem in view of the operation and quality in that tubes of the heat exchanger are clogged with polymer scale or polymers in the form of blocks produced in the polymerization vessel and in the circulation path comprising the heat exchanger and a pipeline connecting the heat exchanger and the polymerization vessel or where the obtained polymer is molded, for example, into a sheet, fish eyes increase.
Therefore, the present inventors found a method wherein a strainer is arranged in the course of the pipeline to catch peeled polymer scale and polymers in the form of blocks. However, although this method can prevent the tubes of the heat exchanger from being clogged until the polymerization are repeated in about 2 or 3 batches, where the number of batches of the polymerization exceeds the above number, the filter installed in the strainer is clogged with paperlike scale to cause the flow velocity of the reaction mixture to drop and finally the circulation of the reaction mixture is stopped in some cases, which is a disadvantage.